The present invention relates to a cylinder head for a direct-injection internal-combustion engine and, more particularly, to a cylinder head having injection valves which are accommodated in openings in the cylinder head and are secured in pairs by one fastening element respectively constructed as a hold-down device on the cylinder head, the hold-down device having two holding or fastening arms for the two injection vales and being fastened to the cylinder head by way of a central fastening point.
Hold-down devices for fuel injection valves of direct-injection internal-combustion engines are known, for example, from EP 0 775 820 B1. Such hold-down devices are fastened by a central fastening point at the cylinder head, and by way of their two holding arms, press two fuel injection valves into the opening provided in the cylinder head. The fuel lines connected to the injection valves permit static as well as dynamic forces to be exercised upon the injection valves during the operation of the internal-combustion engine. Vibrations caused by internal and external influences should be absorbed to a certain degree by the hold-down devices as well as the injection valves.
It is therefore an object of the invention to fasten the fuel injection valves by a corresponding hold-down device fastening arrangement in an operationally reliable and durable manner at or in the cylinder head. Loads acting upon the injection valve are to be reduced.
This object has been achieved by dome-type receiving devices constructed on the two arms of the hold-down device, in which the connection piece of the fuel injection valve is in each case elastically disposed. As a result, a durable and operationally reliable fastening of the fuel injection valves at the cylinder head is ensured—despite the occurring vibrations. Furthermore, the dynamic and static loads upon the injection valves are reduced.
The two dome-type receiving devices of the hold-down device each have an opening in which a section of the fuel connection piece is form-lockingly received. The form-locking receiving is used for supporting the screw-down torque of swivel nuts for fuel feed lines which are screwed onto the fuel connection piece of the injection valve.
In order to be able to compensate possible position tolerances of the two fuel injection valves in the direction of the cylinder axis (Z-axis), the central fastening of the hold-down device on the cylinder head has devices for the tolerance compensation according to the so-called balance arm principle.
For the tolerance compensation of the two injection valves in the Z-direction, a central opening is made in the hold-down device, in which opening a distance bush is received through which a fastening screw is guided which is screwed to the cylinder head. Coaxially to the distance bush, a spring element is received in a central recess of the hold-down device, which spring element, compressed by way of the head of the fastening screw, is supported on the bottom of the central recess.
The spring element is constructed as a cup spring or as stack of cup springs. The hold-down device is constructed as an aluminum casting. In addition to weight advantages, the casting can within certain limits dampen vibrations introduced by way of the fuel feeding system.
In order to permit an angular alignment of the fuel injection valves to the combustion chamber, the valve body of the injection valve accommodated in the opening of the cylinder head has a seat surface provided with a bevel, which seat surface interacts with an intermediate ring consisting, for example, of plastic material or high-grade steel. The intermediate ring is inserted in the opening for the injection ring constructed as a step-type bore.
On the side interacting with the seat surface of the valve body, the intermediate ring is provided with a crowned surface. This permits a tolerance compensation in the direction of the Y-axis according to the principle of a pivoting bearing.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.